|Sometimes registry error reports turn out to be bad RAM. If you can get inside try cleaning the RAM edge connectors with a pencil eraser, then pop the sticks in and out a few times to clear any oxide off the edge connectors. There are also free RAM checkers around which can run from CD or flash drive.|
If that doesn't help then you could get some further idea about the hardware situation by booting with a Linux Live CD (assuming it has a CD drive). I use Puppy Linux for this. You would have to download it on another computer then create a CD from the image (iso) file - most burner software has a facility for this. You then go to BIOS on your garage sale computer and ensure the CD drive is ahead of the HDD when booting. Pop in the CD and see if it boots to Linux. This only uses the RAM and the CD, leaving your Windows operating system intact.
It will tell you if the RAM is useable and you can look at the HDD via Linux to see what is on there. It will help determine whether this is a hardware or software issue, which at this stage is not 100% certain.
I overlapped with response #1 due to slow typing LOL.
Please do not post then vanish - let us know the outcome